One or more ultrasonic sensors may be mounted on an automotive vehicle, for example a hybrid electric vehicle (HEV), enabling a distance determination between the sensor and an external object. Such an ultrasonic sensor may consist of at least a piezoelectric disc and a membrane, configured to convert electrical energy into mechanical energy, and mechanical energy into electrical energy. More specifically, an oscillated voltage may be applied to the piezo disc such that the piezo disc and membrane vibrate and generate ultrasonic waves at a frequency based on the frequency of voltage oscillation. After the waves are emitted, sensors wait for echoes to come back from objects, and when the echoes interact with the sensor/membrane, the membrane is excited to vibrate. The piezo disc attached to the membrane converts the vibration to voltage, and based on the timeframe of sending and receiving the ultrasonic wave, a distance determination to an object may be inferred.
In a vehicle, ultrasonic sensors may be utilized for inferring distance between a vehicle and obstacles during either assisted, or fully automated parking, for example. However, there are a number of factors that may affect optimal operation of an ultrasonic sensor. Such factors may include temperature, humidity, target surface angle, and reflective surface roughness. Of these four variables, determining humidity in a vehicle may be complicated, particularly in a case where a vehicle may not include a dedicated humidity sensor.
US Patent Application US 20060196272 teaches the use of an ultrasonic sensor configured to transmit two different frequencies, and estimate humidity based on a difference between attenuation losses obtained from the two different frequencies. However, the inventors herein have recognized potential issues with such systems. As one example, US 20060196272 does not teach methods for selecting which ultrasonic sensor to use for conducting a relative humidity measurement, in a condition where a plurality of ultrasonic sensors are positioned on the vehicle.
Furthermore, in some examples, ultrasonic sensors may be utilized to detect an object that is close to a rear of a vehicle, for instance prior to a diesel particulate filter (DPF) regeneration procedure in a vehicle powered by diesel fuel. More specifically, US Patent Application US 2012/0023910 teaches controlling regeneration of a DPF based on whether an object is detected within a threshold distances of the vehicle exhaust. However, the inventors have additionally recognized potential issues with such a system. For example, US 2012/0023910 does not teach the potential for adjusting distance thresholds in order to control DPF regeneration events.
Thus, the inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method is provided, comprising selecting one of a plurality of sensors positioned around a motor vehicle; transmitting a plurality of signals from the selected sensor, each at a different frequency; receiving reflected signals of the transmitted signals; determining attenuation values only for each of the reflected signals which have the same transit time from transmission to receipt; determining differences between pairs of the attenuation values; and converting the differences to an indication of relative humidity.
As one example, the method includes regenerating a particulate filter coupled to an underbody of the motor vehicle by causing burning of particulate stored in the particulate filter resulting in hot gases exiting a rear of the motor vehicle; selecting the selected sensor based on a transmission path of the selected sensor overlapping at least a portion of the hot gases exiting the rear of the motor vehicle; and postponing or aborting the regeneration based on there being an object within a predetermined distance of the hot gases exiting the rear of the motor vehicle. In an example, the method may further include measuring an air temperature near where the hot gases exit the rear of the motor vehicle; determining thermal conductivity of air based, at least in part, on the indication of relative humidity and the air temperature; and adjusting a distance threshold for the regeneration procedure, where the adjusting the distance threshold includes decreasing the distance threshold as thermal conductivity decreases, and increasing the distance threshold as thermal conductivity increases. In this way, a suitable sensor may be selected from a plurality of ultrasonic sensors for determining relative humidity, such that a measurement of relative humidity may be determined. Furthermore, responsive to the indication of relative humidity, the relative humidity measurement may be utilized to adjust a distance threshold for DPF regeneration, which may thus result in greater completion frequency for DPF regeneration events.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.